Azimuth sensors in wind turbines

Abstract

To provide methods and systems for determining reliability or correct functioning of azimuth sensors.SOLUTION: The present disclosure relates to methods for determining reliability of an azimuth measurement system in a wind turbine. The methods comprise measuring loads with load sensors during operation, and determining in-plane moments with rotor rotational speed frequency of one or more blades based on the measured loads. The methods further comprise measuring an azimuthal position of a wind turbine rotor. The method also comprises determining that the azimuth measurement system has reduced reliability if an angular phase of the in-plane moments deviates from the measured azimuthal position by more than a first threshold value. The present disclosure also relates to wind turbine systems incorporating azimuth measurement, and methods for on-line determination of correct functioning of azimuth sensors.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to wind turbines, and more particularly to methods and systems for determining the reliability or correct functioning of azimuth sensors in wind turbines. [Background technology]

[0002] Modern wind turbines are used to supply electricity to the power grid. A wind turbine typically includes a tower with a nacelle supported on top of the tower. A wind turbine rotor, including a hub and a number of wind turbine blades, may be rotatably mounted to the nacelle.

[0003] The wind turbine blades may be set in motion by the wind. The hub of the wind turbine may be operatively coupled to the rotor of a generator. As the hub and blades rotate, the kinetic energy of the wind is converted into kinetic mechanical energy of the wind turbine rotor and ultimately into electrical energy or power in the generator. The generator may typically be located inside a nacelle.

[0004] The wind turbine rotor can be directly coupled to the generator rotor in so-called direct drive wind turbines. Alternatively, the wind turbine rotor may include a main rotor shaft (so-called "low speed shaft") that leads to a gearbox. A high speed shaft of the gearbox can then drive the generator. Regardless of the wind turbine topology, the power output from the generator can be fed into the power grid. The connection of the generator to the power grid can include, for example, converters, transformers, medium voltage lines, etc.

[0005] A wind turbine controller can be configured to determine appropriate actuator setpoints for the wind turbine based on ambient conditions. Actuator setpoints for modern variable speed wind turbines include, for example, generator torque and blade pitch angle. By controlling the blade pitch angle and generator torque, the rotor speed can be controlled, as well as power output, aerodynamic thrust, and additional mechanical loads. The objective of the control system is generally to maximize power output while simultaneously maintaining loads on the wind turbine at acceptable levels.

[0006] As mentioned above, the actuator set points for torque and pitch (and also other actuators such as yaw) can be changed depending on the situation. Important inputs for determining the actuator set points include, for example, wind speed and direction. Wind speed can be measured directly or indirectly, for example, through the use of a (generator) rotor speed sensor.

[0007] Additionally, wind turbines can include load sensors on or in the blades to measure loads on the blades caused, for example, by wind and / or the weight of the blades. Excessive loads on the blades can, for example, damage the blades and / or cause the rotor to rotate at an undesirable speed, damaging other components of the wind turbine. Blade load sensors can detect high loads and react, for example, by activating the pitch system in a way that can reduce the loads on the blades. These adjustments of the blades by the pitch system can extend the life of the wind turbine and / or reduce the cost of generating electricity.

[0008] Load sensors for measuring loads on wind turbines, and in particular on wind turbine blades, may include resistive strain gauges, fiber optic strain gauges, or any other known strain sensing system.

[0009] For wind turbine blades, various blade loads can be defined: edgewise, spanwise, and flapwise. The spanwise direction refers to the direction along the longitudinal axis of the blade, extending from the blade root to the blade tip. The edgewise direction refers to the direction along the chord of a section of the wind turbine blade, extending from the leading edge to the trailing edge. The flapwise direction is perpendicular to both the edgewise and spanwise directions.

[0010] For a wind turbine rotor, loads can be decomposed into in-plane loads (loads tangential to the rotor plane) and out-of-plane loads (loads normal to the rotor plane). The rotor plane may be defined herein as the plane normal to the rotor axis of rotation and passing through the centre of the blade at the blade root.

[0011] An additional sensor that can be used in the operation of a wind turbine is an azimuth sensor. The azimuth angle represents the angular position of the wind turbine rotor in the rotor plane. While any particular reference position can be selected, in one example, at the 0° position, one of the blades may be at the 12 o'clock position (pointing straight up). In a three-bladed rotor, the remaining two blades may be at the 4 o'clock and 8 o'clock positions, respectively. Following the same reference position, at the 90° position of the rotor, the three blades are at the 3 o'clock position (substantially horizontal), the 7 o'clock position, and the 11 o'clock position, respectively.

[0012] An azimuth sensor, as used throughout this disclosure, is any suitable sensor or sensor system that can be used to measure the azimuth position of a rotor. In one example, the azimuth sensor may be an encoder fixed to the wind turbine rotor shaft or generator rotor.

[0013] Therefore, accurate functioning of the azimuth sensor is important for wind turbine operation in general, and for certain maintenance operations in particular. For example, individual blade pitch control can be based on signals from the azimuth sensor. In rotor locking operations, the wind turbine rotor must be accurately positioned in one of several predetermined positions so that a locking mechanism on the nacelle can engage the wind turbine rotor (hub) and maintenance can be performed.

[0014] Azimuth sensors can be calibrated to maintain accuracy. Calibration typically involves establishing a correspondence between the indications produced by the azimuth sensor and a reference value according to a calibration pattern (i.e., specific conditions for calibration). Such calibrations are generally performed offline (i.e., when the wind turbine is not operating) and require specific conditions (no wind or very low wind speeds). In some instances, a visual inspection by personnel on the ground may be required to determine if the rotor is in a specific operation.

[0015] It is known that azimuth sensors can degrade over time. In particular, it has been shown that azimuth sensors can exhibit error "drift" behavior, i.e., the difference between the actual angular position of the rotor and the indicated position increases over time. It has also been shown that offsets can be introduced into the system after maintenance operations.

[0016] Incorrect azimuth sensor indications may result in inadequate or non-optimal load control and / or inadequate or non-optimal individual or aggregate pitch control, resulting in increased (fatigue) loads and / or reduced energy output. Incorrect azimuth sensor indications may result in increased complexity and maintenance times.

[0017] The present disclosure provides example methods and systems for determining the reliability or accurate functioning of an azimuth sensor that address at least some of the above-mentioned shortcomings. Summary of the Invention

[0018] In a first aspect, a method for determining reliability of an azimuth measurement system in a wind turbine is provided. The method includes measuring a load with a load sensor during operation of the wind turbine and determining an in-plane moment having a rotor rotational speed frequency of one or more blades based on the measured load. The method then further includes determining an angular phase of the wind turbine rotor based on the in-plane moment having the rotor rotational speed frequency, and determining that the reliability of the azimuth measurement system has decreased if the angular phase of the in-plane moment having the rotor rotational speed frequency deviates from the angular phase measured by the azimuth measurement system by more than a first threshold.

[0019] According to this aspect, the reliability or accurate functioning of the azimuth sensor can be determined during wind turbine operation, i.e., it is possible to determine whether the azimuth measurement system accurately indicates the azimuth position without having to interrupt the operation of the wind turbine or subject it to specific conditions. The measured loads may be measured as or converted to in-plane moments. The in-plane moment at any given moment during operation is a combination of aerodynamic loads and loads due to the mass of the blade. However, the mass of the blade contributes the same moment with each rotation of the blade. At the 12 o'clock and 6 o'clock positions, the mass of the blade does not contribute to the bending moment. However, at the 3 o'clock and 9 o'clock positions, the bending moment due to the mass of the blade is maximized (in one direction and in the opposite direction, respectively). The mass of the blade has a clearly defined contribution at the 1p frequency, i.e., fluctuations in the moment due to the mass have the same frequency as the rotor rotation speed. In this context, rotor refers to the wind turbine rotor, not the generator rotor. The generator rotors may have the same rotational speed in the case of direct drive wind turbines, but may have very different speeds in the case of wind turbines with gearboxes.

[0020] The terms "1p frequency" and "rotor rotational speed frequency" may be used interchangeably throughout this disclosure.

[0021] By selecting an in-plane moment having a rotor rotational speed frequency and comparing the angular phase of the selected in-plane moment with the measured azimuth phase angle, a deviation between the two signals a possible malfunction of the azimuth measurement system. When such a possible malfunction is detected, various measures can be taken to reduce the risk of a malfunctioning azimuth measurement system.

[0022] Non-limiting examples of the present disclosure are described below with reference to the accompanying drawings. [Brief explanation of the drawings]

[0023] [Figure 1] 1 illustrates a perspective view of a wind turbine according to an example. [Figure 2] 1 illustrates a detailed internal view of a nacelle of a wind turbine according to an example. [Figure 3] 1 illustrates a schematic diagram of an example of a method for determining the reliability of an azimuth measurement system in a wind turbine. [Figure 4] 10 shows a schematic of an example of a comparison between the in-plane moment due to the mass of a rotor blade and the measured azimuth position. [Figure 5] 10 illustrates schematically another example of a method for determining reliability of a wind turbine azimuth measurement system. [Figure 6] 1 illustrates schematically a method for determining the exact functionality of an azimuth sensor online that may be implemented in a wind turbine controller. [Figure 7A] 10 shows a schematic comparison between measured in-plane moments and theoretical in-plane moments based on measured azimuth angles. [Figure 7B] 10 shows a schematic comparison between measured in-plane moments and theoretical in-plane moments based on measured azimuth angles. DETAILED DESCRIPTION OF THE INVENTION

[0024] Reference will now be made in detail to the embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided as an illustration of the invention, not as a limitation of the invention. Indeed, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For example, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. It is therefore intended that the present invention cover such modifications and variations as come within the scope of the appended claims and their equivalents.

[0025] FIG. 1 is a perspective view of an example wind turbine 10. In this example, wind turbine 10 is a horizontal axis wind turbine. Alternatively, wind turbine 10 may be a vertical axis wind turbine. In this example, wind turbine 10 includes a tower 100 extending from a support system 14 on ground 12, a nacelle 16 mounted on tower 100, and a rotor 18 coupled to nacelle 16. Rotor 18 includes a rotatable hub 20 and at least one rotor blade 22 coupled to and extending outward from hub 20. In this example, rotor 18 has three rotor blades 22. In alternative embodiments, rotor 18 includes more or fewer than three rotor blades 22. Tower 100 may be fabricated from tubular steel to define a cavity (not shown in FIG. 1 ) between support system 14 and nacelle 16. In alternative embodiments, tower 100 is any suitable type of tower having any suitable height. According to alternatives, the tower may be a hybrid tower comprising a concrete section and a tubular steel section, or the tower may be a partial or complete lattice tower.

[0026] The rotor blades 22 are spaced about the hub 20 to facilitate rotation of the rotor 18 and convert kinetic energy from the wind into usable mechanical energy, which can then be converted into electrical energy. The rotor blades 22 are coupled to the hub 20 by coupling their blade roots 24 to the hub 20 at a number of load transfer areas 26. The load transfer areas 26 may include hub load transfer areas and blade load transfer areas (both not shown in FIG. 1 ). Loads induced on the rotor blades 22 are transferred to the hub 20 via the load transfer areas 26.

[0027] In some examples, rotor blades 22 can have lengths ranging from approximately 15 meters (m) to approximately 90 m or more. Rotor blades 22 can have any suitable length that enables wind turbine 10 to function as described herein. For example, example blade lengths include, but are not limited to, lengths of 20 m or less, 37 m, 48.7 m, 50.2 m, 52.2 m, or greater than 91 m. When wind impinges on rotor blades 22 from wind direction 28, rotor 18 rotates about rotor axis 30. As rotor blades 22 rotate and experience centrifugal forces, rotor blades 22 also experience various forces and moments. Thus, rotor blades 22 may deflect and / or rotate from a neutral or unbiased position to a biased position.

[0028] Furthermore, the pitch angle of the rotor blades 22, i.e., the angle at which the rotor blades 22 are oriented relative to the wind direction, can be varied by the pitch system 32 to adjust the angular position of at least one rotor blade 22 relative to the wind vector, thereby controlling the load and the power generated by the wind turbine 10. A pitch axis 34 of the rotor blade 22 is shown. During operation of the wind turbine 10, the pitch system 32 can vary the pitch angle of the rotor blades 22, in particular to reduce the angle of attack of (parts of) the rotor blades, which can facilitate reducing the rotational speed and / or facilitating stalling of the rotor 18.

[0029] In this example, the blade pitch of each rotor blade 22 is individually controlled by the wind turbine controller 36 or pitch control system 80. Alternatively, the blade pitch of all rotor blades 22 may be simultaneously controlled by the control system.

[0030] Additionally, in this example, as wind direction 28 changes, the yaw direction of nacelle 16 can be rotated about yaw axis 38 to position rotor blades 22 relative to wind direction 28 .

[0031] Although in this example wind turbine controller 36 is shown as centralized within nacelle 16, wind turbine controller 36 may be a distributed system located throughout wind turbine 10, on support system 14, within the wind farm, and / or at a remote control center. Wind turbine controller 36 includes a processor 40 configured to perform the methods and / or steps described herein. Additionally, many of the other components described herein include a processor.

[0032] As used herein, the term "processor" is not limited to integrated circuits technically referred to as computers, but refers broadly to controllers, microcontrollers, microcomputers, programmable logic controllers (PLCs), application specific integrated circuits, and other programmable circuits, and these terms are used interchangeably herein. It should be understood that the processor and / or control system may further include memory, input channels, and / or output channels.

[0033] 2 is an enlarged cross-sectional view of a portion of wind turbine 10. In this example, wind turbine 10 includes a nacelle 16 and a rotor 18 rotatably coupled to nacelle 16. More specifically, a hub 20 of rotor 18 is rotatably coupled to a generator 42 located within nacelle 16 by a main shaft 44, a gearbox 46, a high-speed shaft 48, and a coupling 50. In this example, main shaft 44 is disposed at least partially coaxially with a longitudinal axis (not shown) of nacelle 16. Rotation of main shaft 44 drives gearbox 46, which in turn drives high-speed shaft 48 by converting the relatively slow rotational motion of rotor 18 and main shaft 44 into relatively fast rotational motion of high-speed shaft 48. The latter is connected to generator 42 for producing electrical energy with the aid of coupling 50. Additionally, a transformer 90 and / or appropriate electronics, switches, and / or inverters may be disposed within the nacelle 16 to convert the electrical energy generated by the generator 42, having a voltage between 400V and 1000V, into electrical energy having a medium voltage (e.g., 10-35 kV) or even a higher voltage, such as 66 kV. The electrical energy is conducted from the nacelle 16 to the tower 100 via a power cable 160.

[0034] The gearbox 46, generator 42, and transformer 90 may be supported by a main support structure frame of the nacelle 16, which is optionally embodied as a main frame 52. The gearbox 46 may include a gearbox housing connected to the main frame 52 by one or more torque arms 103. In this example, the nacelle 16 further includes a main forward support bearing 60 and a main aft support bearing 62. Additionally, the generator 42 may be attached to the main frame 52 by an isolation support means 54, particularly to prevent vibrations of the generator 42 from being introduced into the main frame 52 and thereby causing a source of noise emissions.

[0035] Optionally, the main frame 52 is configured to carry the weight of the rotor 18 and nacelle 16 components, as well as the overall loads caused by wind and rotational loads, and to introduce these loads into the tower 100 of the wind turbine 10. The rotor shaft 44, generator 42, gearbox 46, high-speed shaft 48, coupling 50, and any associated fastening, supporting, and / or securing devices, such as, but not limited to, supports 52, forward support bearing 60, and aft support bearing 62, may be referred to as a drive train 64.

[0036] Additionally, the nacelle 16 may include a yaw drive mechanism 56 that may be used to rotate the nacelle 16, and thus the rotor 18, about the yaw axis 38 to control the viewpoint of the rotor blades 22 relative to the wind direction 28.

[0037] To properly position the nacelle 16 relative to the wind direction 28, the nacelle 16 may further include at least one meteorological measurement system, which may include a wind vane and an anemometer. The meteorological measurement system 58 may provide information, which may include the wind direction 28 and / or wind speed, to the wind turbine controller 36. In this example, the pitch system 32 is at least partially disposed within the hub 20 as a pitch assembly 66. The pitch assembly 66 includes one or more pitch drive systems 68 and at least one sensor 70. Each pitch drive system 68 is coupled to a respective rotor blade 22 (shown in FIG. 1 ) to adjust the pitch angle of the rotor blade 22 along the pitch axis 34. Only one of the three pitch drive systems 68 is shown in FIG. 2 .

[0038] In this example, pitch assembly 66 includes at least one pitch bearing 72 coupled to hub 20 and each rotor blade 22 (shown in FIG. 1 ) to rotate each rotor blade 22 about pitch axis 34. Pitch drive system 68 includes a pitch drive motor 74, a pitch drive gearbox 76, and a pitch drive pinion 78. Pitch drive motor 74 couples to pitch drive gearbox 76 such that pitch drive motor 74 imparts a mechanical force to pitch drive gearbox 76. Pitch drive gearbox 76 couples to pitch drive pinion 78 such that pitch drive gearbox 76 rotates pitch drive pinion 78. Pitch bearing 72 couples to pitch drive pinion 78 such that rotation of pitch drive pinion 78 causes rotation of pitch bearing 72.

[0039] Pitch drive system 68 couples to wind turbine controller 36 to adjust the pitch angle of rotor blades 22 upon receiving one or more signals from wind turbine controller 36. In this example, pitch drive motor 74 is any suitable motor driven by an electrical and / or hydraulic system that enables pitch assembly 66 to function as described herein. Alternatively, pitch assembly 66 may include any suitable structure, configuration, arrangement, and / or components, such as, but not limited to, hydraulic cylinders, springs, and / or servo mechanisms. In certain embodiments, pitch drive motor 74 is driven by the rotational inertia of hub 20 and / or energy extracted from a stored energy source (not shown) that provides energy to components of wind turbine 10.

[0040] Pitch assembly 66 may further include one or more pitch control systems 80 for controlling pitch drive systems 68 according to control signals from wind turbine controller 36 for certain priority conditions and / or in the event of rotor 18 overspeed. In this example, pitch assembly 66 includes at least one pitch control system 80 communicatively coupled to each pitch drive system 68 for controlling pitch drive systems 68 independently from wind turbine controller 36. In this example, pitch control system 80 couples to pitch drive systems 68 and sensors 70. During normal operation of wind turbine 10, wind turbine controller 36 may control pitch drive systems 68 to adjust the pitch angle of rotor blades 22.

[0041] According to one embodiment, a power supply 84, comprising, for example, a battery, an electrical capacitor, or a generator driven by the rotation of the hub 20, is disposed at or within the hub 20 and is coupled to the sensor 70, the pitch control system 80, and the pitch drive system 68 to provide a source of electrical power to these components. In this example, the power supply 84 provides a continuous source of electrical power to the pitch assembly 66 during operation of the wind turbine 10. In an alternative embodiment, the power supply 84 provides electrical power to the pitch assembly 66 only during a loss-of-power event of the wind turbine 10. The loss-of-power event may include a loss or degradation of the electrical grid, a malfunction in the electrical system of the wind turbine 10, and / or a failure of the wind turbine controller 36. During a loss-of-power event, the power supply 84 operates to provide electrical power to the pitch assembly 66 so that the pitch assembly 66 can operate during the loss-of-power event.

[0042] In this example, each of pitch drive system 68, sensor 70, pitch control system 80, cables, and power supply 84 is disposed within a cavity 86 defined by an inner surface 88 of hub 20. In alternative embodiments, the components may be disposed relative to and directly or indirectly coupled to the outer surface of hub 20.

[0043] 3 illustrates a schematic diagram of an example method for determining the reliability of an azimuth measurement system in a wind turbine. The method includes measuring loads with load sensors during operation of the wind turbine in block 200. In block 210, an in-plane moment based on the measured loads is determined. Then, in block 220, an in-plane moment having a 1p frequency is selected.

[0044] The azimuth angle of the wind turbine rotor is measured in block 250. The selected in-plane moment phase angle may be compared to a theoretical in-plane moment phase angle due to the mass of the blade in block 230. Then, in block 240, it may be determined that the reliability of the azimuth measurement system is degraded if the selected in-plane moment phase angle deviates from the theoretical in-plane moment phase angle by more than a first threshold.

[0045] In some examples, the theoretical in-plane moment due to the mass of one or more blades derived from the azimuth phase angle can be compared to the selected in-plane moment phase angle to determine (reduction in) reliability.

[0046] In some examples, measuring the loads in block 200 can include measuring flapwise and edgewise moments. A standard wind turbine blade can be equipped with an appropriate load sensor. The load sensor can be a strain gauge. Depending on the location and method of attachment of the load sensor, strains in different directions can be measured. Sensors located on the hub or any other (indirect) blade support can also be used to determine the load.

[0047] The edgewise and flapwise loads can be used to control the wind turbine. In block 210, the edgewise and flapwise moments can be converted to in-plane and out-of-plane moments based on the blade pitch angle. Since the loads on the rotor wind turbine blade mass are in-plane loads, not out-of-plane loads, only the in-plane moments need be considered in the method.

[0048] Selecting the in-plane moment having the rotor rotational speed frequency in block 220 may include filtering the determined in-plane moment using a peak filter. A peak filter is a frequency filter configured to pass a narrow frequency band and block all other frequencies. A peak filter in this respect is essentially a very narrow bandpass filter. The results of the filter can be seen in the top part of FIG. 4, which shows the in-plane mode having a 1p frequency for three blades of a wind turbine over several revolutions of the wind turbine rotor.

[0049] From the selected in-plane moments, the phase angle for each individual blade can be derived. For each individual blade, the maximum moment corresponds to the corresponding 3 o'clock position of the blade, and the minimum moment (or most negative moment) corresponds to the 9 o'clock position of the blade.

[0050] If the azimuth measurement system is functioning correctly, the moment due to the mass of the blade should match the theoretical moment that would be caused by the mass of the blade at the measured azimuth position. In other words, if the azimuth measurement system is functioning correctly, the phase angle of the moment due to the mass of the blade should match the measured azimuth angle. The measured azimuth angle is shown in the center of Figure 4.

[0051] The phase angle difference is shown for each individual blade at the bottom of Figure 4. The phase angle difference can be determined continuously, or, as in the example of Figure 4, can be determined once per revolution.

[0052] In the example of Figure 4, individual rotor blades exhibiting a misalignment between their measured azimuth angle and the azimuth angle derived from the load analysis are between -2° and 5°. In this particular example, two different angle thresholds are defined.

[0053] In block 240, if the selected in-plane moment phase angle deviates from the theoretical in-plane moment phase angle by more than a first threshold, it can be determined that the azimuth measurement is unreliable.

[0054] In some examples, the first threshold may be an angle between 6° and 15°, specifically between 8° and 15°. In Figure 4, the first threshold is selected to be 10°.

[0055] In some examples, the angle difference comparison can be determined for each blade individually. The angle difference for each blade can be compared to an acceptable maximum or threshold. In other examples, the average of the blade phase angle differences can be compared to a threshold.

[0056] In some examples, the method can further include generating a warning signal or modifying operation of the wind turbine when the reliability of the azimuth measurement system is determined to be degraded. Modifying operation of the wind turbine can include one or more of reducing a power level of the wind turbine, disabling or modifying one or more control algorithms that rely on measurements from the azimuth measurement system.

[0057] In some examples, the method can further include generating a first alarm signal if the azimuth measurement system becomes unreliable. A first threshold can be defined to signal a malfunction. Various actions can be taken if the threshold is exceeded. Maintenance can be scheduled to replace or recalibrate the sensor. Alternatively, operation of the wind turbine can be modified to a reduced output level, i.e., the load on the wind turbine can be intentionally reduced at the expense of power generation because the sensor measurements are not as reliable as they should be. In still further examples, control algorithms and methods that rely on input from the azimuth sensor can be disabled and / or replaced with other algorithms and methods. In other examples, operation of the wind turbine can be stopped if the azimuth sensor is determined to be unreliable. In some examples, different threshold levels (two or more) can be defined, with different actions for each threshold defined, including alarm signals, scheduling maintenance or recalibration, disabling or adjusting control functions, controls to reduce load, suspending operation, etc.

[0058] In some examples, as shown in FIG. 4 , the method may further include determining whether the angular phase of the in-plane moment with the rotor rotational speed frequency of one or more blades deviates from the theoretical in-plane moment angular phase by more than a second threshold value that is greater than the first threshold value.

[0059] The second threshold may be between 10° and 20°. In the particular example of FIG. 4, the second threshold is fixed at 15°. In some examples, the method may further include suspending operation of the wind turbine if the phase angle of the selected in-plane moment of the blade deviates from the theoretical in-plane moment phase angle of the blade by more than the second threshold. In these examples, the first threshold may generate a warning signal (notifying the operator of a potential problem and allowing operation to continue as normal or with some modifications), while passing the second threshold indicates a more serious warning (e.g., suspending operation, reducing the level of operation, etc.).

[0060] In a further aspect, a wind turbine system is provided. Referring to Figure 1, the wind turbine system comprises a wind turbine 10 including a wind turbine rotor 18 with a plurality of blades 22, a plurality of load sensors for measuring loads on the blades 22, and an azimuth measurement system for determining the angular position of the wind turbine rotor 18 in the rotor plane.

[0061] The wind turbine system further comprises a control system configured to perform any of the methods presented herein.

[0062] 6, in particular, the control system may be configured to receive signals from load sensors during operation at block 400. Additionally, the control system may determine an in-plane moment in one or more of the blades at block 410. In particular, an in-plane moment having a frequency of 1p may be determined or selected at block 410.

[0063] Additionally, the control system may be further configured to receive azimuth positions from one or more azimuth sensors at block 420. Furthermore, the control system may be configured to compare the phase angle of the selected in-plane moment with the measured azimuth phase angle to determine whether the phase angle of the selected in-plane moment deviates from the measured azimuth phase angle by more than a predetermined threshold. If this determination is made, a degradation in the reliability of the azimuth sensor is detected at block 440. The control system may be further configured to generate a warning signal if a degradation in reliability is detected. As previously mentioned, the warning signal can take various forms and can result in various actions, including scheduling maintenance, replacing or recalibrating the sensor, suspending operation, sending an alert to a remote operation center, etc. In a further example, inputs from azimuth sensors that can still be deemed reliable can be selected as inputs (ignoring inputs from other azimuth sensors).

[0064] 7A and 7B show a schematic comparison between the measured in-plane moment and the theoretical in-plane moment based on the measured azimuth angle.

[0065] In the situation shown in Figure 7A, a comparison is made between the measured in-plane moment (bold line) and the theoretical in-plane moment (dashed lines indicate upper and lower thresholds) for three individual blades based on the measured azimuth angle. That is, an indirect comparison is made between the phase angle that can be derived from the measured in-plane moment and the phase angle measured by the azimuth sensor. It can be seen (right side of the figure) that in the situation shown in Figure 7A, the phase angle difference is generally in the range between +5° and -5°. In a specific example, the first threshold is shown set at 10° and the second threshold is shown set at 15°. The difference in results between individual blades can generally be explained by the precision or error of the measurements.

[0066] Instead, in the situation of Figure 7B, it can be seen that there is a large difference of about 30° between the measured azimuth angle and the angle that can be derived from the load measurements. Furthermore, it can be seen that this deviation is seen not only for a single blade (which could signal a possible problem in the measurement of a single blade), but for each of the three blades.

[0067] Even though load sensors can sometimes be unreliable, it has been found that such unreliability typically affects the absolute value of the measurement but not the phase angle significantly. Therefore, the example method presented herein can be used even when the load sensors are somewhat unreliable.

[0068] In some examples, each blade may be equipped with a strain gauge. In particular, some strain gauges may be positioned to measure flapwise moments and other strain gauges may be positioned to measure edgewise moments. The strain gauges may be positioned at or near the root of the blade where the bending moment is greatest. In other examples, the strain gauges may be positioned at spanwise locations away from the root. In some examples, measurements from such strain gauges may be converted to moments at the blade root. In some examples, measurements from load sensors on blades that are not at the root may be extrapolated to indicate the moment at the blade root. In some examples, sensors may be mounted at appropriate locations on the hub instead of on the blades.

[0069] In other examples, other sensors or systems can be used to measure stress and strain and / or derive the bending moment of the blade. Suitable strain gauges can include resistive foil strain gauges. The resistive strain gauges can be attached to the blade with a suitable adhesive, such as an epoxy adhesive. Other types of strain gauges and sensors can also be used, such as piezoresistors, capacitive strain gauges, or fiber optics for measuring strain along an optical fiber, or accelerometers.

[0070] In some examples, the azimuth measurement system includes a rotary encoder. Such a rotary encoder can be disposed with the wind turbine rotor or hub, including the low-speed shaft. Additionally, the rotary encoder can be disposed with the generator rotor or high-speed shaft. In a further example, the azimuth measurement system can be based on, for example, a capacitance, inductance, magnetic, or proximity sensor disposed with the hub. Such a sensor can measure the interaction of the hub with a nacelle mounting element to determine the azimuth angle.

[0071] In some examples, the control system may be located remotely from the wind turbine. The control system may be part of a wind farm's SCADA system or may be located in a remote operation center. In some examples, the wind turbine controller itself may be equipped with functionality for determining the potential malfunction or loss of reliability of a load sensor. Furthermore, the control system may form part of the wind turbine controller, i.e., a combination of hardware and / or software provided on the wind turbine itself.

[0072]

[0023] Figure 5 illustrates schematically another example of a method for determining the reliability of a wind turbine azimuth measurement system. Figure 5 illustrates schematically a method for determining the correct functionality of a wind turbine's azimuth sensors online. An "online" determination may be considered herein as a determination made substantially in real time during normal operation of the wind turbine. Thus, the determination does not require a specific operating sequence or specific operating conditions.

[0073] The method includes measuring edgewise and flapwise strains on the wind turbine blade at block 300. The method then includes determining edgewise and flapwise bending moments on the wind turbine blade based on the measured strains at block 310.

[0074] In block 320, the determined edgewise and flapwise bending moments may be converted to measured in-plane and out-of-plane moments on the wind turbine blade. The conversion from edgewise and flapwise to in-plane and out-of-plane may be based on, among other things, the pitch angle of the individual blade. In block 330, a peak filter may be applied to determine the measured in-plane moment having the 1p frequency. Then, in block 340, the angular phase of the in-plane moment at the 1p frequency may be determined.

[0075] The method includes measuring the azimuth angle of the rotor blade with an azimuth sensor at block 350. A phase angle determined based on the measured in-plane moment having a 1p frequency may then be compared to the measured azimuth angle at block 360.

[0076] In block 370, if the angular phase of the measured in-plane moment having the 1p frequency differs from the measured azimuth angle by less than the threshold phase angle difference, the azimuth sensor is determined to be functioning properly. Operation of the wind turbine can continue as normal, as shown schematically in Figure 5. If the angle difference exceeds the threshold, action can be taken to address the azimuth sensor malfunction and / or a warning can be generated.

[0077] Although FIG. 5 illustrates the method for a single blade of a wind turbine, the same method can be applied to multiple blades of the same wind turbine.

[0078] In some examples, the method may further include ceasing operation of the wind turbine if the alert is generated, or reducing the level of operation of the wind turbine if the alert is generated.

[0079] The order shown for the method steps in Figures 3, 5, and 6 should not necessarily be considered sequential. In particular, the determination of the azimuth angle does not need to be performed at any particular moment in time compared to the measurement of the load. The measured load and azimuth angle only need to be correlated in time so that a meaningful comparison can be made. Also, the method may be performed continuously during operation of the wind turbine. The steps may be performed at a frequency greater than 1 Hz, particularly greater than 10 Hz.

[0080] Throughout this disclosure, reference has been made to a comparison between a measured azimuth phase angle and a phase angle that can be derived from an in-plane bending moment having a 1p frequency (i.e., a moment that can theoretically be attributed solely to the weight or mass of the blade). In some cases, such a comparison can be made directly. In other cases, a comparison can be made between the angular phase of a measured in-plane bending moment having a 1p frequency and a theoretical moment caused by the mass of the blade, which can be calculated based on the measured azimuth angle.

[0081] Throughout this disclosure, reference is made to threshold comparisons. Such comparisons may be based on one revolution of the wind turbine rotor. In other examples, the threshold (or thresholds) comparisons may be based on multiple revolutions of the rotor, such as 5, 10, or more.

[0082] Example methods disclosed herein may be implemented in hardware, software, firmware, or any combination thereof.

[0083] Those skilled in the art will further appreciate that the various illustrative logic blocks, modules, circuits, and algorithm steps described in connection with this disclosure can be implemented as electronic hardware, computer software, or a combination of both. To clearly illustrate this interchangeability between hardware and software, the various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends on the particular application and design constraints imposed on the overall system. Those skilled in the art will be able to implement the described functionality in a variety of ways tailored to each particular application.

[0084] The various illustrative logic blocks, modules, and circuits described in connection with the disclosure herein may be implemented or performed by one or more general-purpose processors, digital signal processors (DSPs), cloud computing architectures, application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs) or other programmable logic devices, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. Furthermore, a processor may be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

[0085] Additionally, the present disclosure relates to a computing system configured to perform any of the methods disclosed herein.

[0086] Furthermore, the present disclosure relates to a computer program or computer program product comprising instructions (code) that, when executed, perform any of the methods disclosed herein.

[0087] The computer program may be in the form of object code, such as source code, object code, code intermediate source and partially compiled form, or in any other form suitable for use in the implementation of a process. The carrier may be any entity or device capable of carrying a computer program.

[0088] If implemented in software / firmware, the functions may be stored or transmitted as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media, including any medium that facilitates transfer of a computer program from one place to another. Storage media may be any available medium accessible by a general-purpose or special-purpose computer. By way of example, and not limitation, such computer-readable media may comprise RAM, ROM, EEPROM, CD / DVD or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general-purpose or special-purpose computer or a general-purpose or special-purpose processor. Any connection is also properly termed a computer-readable medium. For example, if the software / firmware is transmitted from a website, server, or other remote source using coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. As used herein, disk and disc include compact discs (CDs), laser discs, optical discs, digital versatile discs (DVDs), floppy disks, and Blu-ray discs, where disks typically reproduce data magnetically while discs reproduce data optically with a laser. Combinations of the above should also be included within the scope of computer-readable media.

[0089] This specification uses examples to disclose the present invention, including preferred embodiments, and to enable those skilled in the art to practice the invention, including making and using any devices or systems and performing any related methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements that do not have substantial differences from the literal language of the claims. Those skilled in the art will be able to mix and match aspects from the various embodiments described above, as well as other known equivalents for each such aspect, to construct further embodiments and techniques consistent with the principles of the present application. Where reference signs relating to the drawings are placed within parentheses in the claims, these reference signs are merely intended to make the claims more readable and should not be construed as limiting the scope of the claims. [Explanation of symbols]

[0090] 10. Wind Turbines 12 Ground 14 Support System 16 Nacelle 18 Wind Turbine Rotor 20 Hub 22 rotor blades 24 Blade base 26 Load Transfer Area 28 Wind direction 30 rotor shaft 32 Pitch System 34 Pitch axis 36 Wind Turbine Controller 38 Yaw axis 40 processors 42 Generator 44 Main shaft, rotor shaft 46 Gearbox 48 High Speed ​​Shaft 50 Coupling 52 Main frame, support 54 Separation support means 56 Yaw drive mechanism 58 Weather Measurement System 60 Front support bearing 62 Rear support bearing 64 Drivetrain 66 Pitch Assembly 68 Pitch Drive System 70 sensors 72 Pitch bearing 74 Pitch drive motor 76 Pitch drive gearbox 78 Pitch drive pinion 80 Pitch Control System 84 Power supply 86 Cavity 88 Inner 90 Transformer 100 Tower 103 Torque arm 160 Power Cable

Claims

1. A method for determining the reliability of an azimuth measurement system in a wind turbine (10), measuring the angular phase of the rotor of the wind turbine (10) by the azimuth measurement system; measuring the load with a load sensor during operation of the wind turbine (10) (step 200); determining an in-plane moment having a rotor rotation speed frequency of one or more blades based on the measured load (step 210); when the angular phase of the in-plane moment having the rotor rotation speed frequency deviates from the angular phase measured by the azimuth measurement system by more than a first threshold value, determining that the reliability of the azimuth measurement system is degraded (step 240); and a method comprising the steps of:

2. The method according to claim 1, wherein the step (200) of measuring the load includes a step (300) of measuring moments in the flap direction and the edge direction.

3. The method according to claim 2, wherein the moments in the flap direction and the edge direction are converted (320) into in-plane moments and out-of-plane moments based on the pitch angle of the blade.

4. The step of determining an in-plane moment having a rotor rotation speed frequency includes: determining an in-plane moment based on the measured load (step 210); selecting an in-plane moment having a rotor rotation speed frequency (step 340); and a method according to claim 1.

5. The method according to claim 4, wherein the step (340) of selecting an in-plane moment having a rotor rotation speed frequency includes a step (330) of filtering the determined in-plane moment of the blade using a peak filter.

6. The method according to claim 1, wherein the first threshold value is an angle between 6 and 15°, specifically between 8 and 15°.

7. The method according to claim 1, comprising the step of comparing the in-plane moment having the rotor rotation speed frequency of each blade with the theoretical in-plane moment due to the mass of each blade based on the measured azimuth position of the wind turbine rotor (18).

8. The method according to claim 7, comprising the step of determining that the reliability of the azimuth measurement system is reduced when the angular phase of the in-plane moment having the rotor rotation speed frequency of at least one of the blades deviates from the angular phase of the theoretical in-plane moment by more than a first threshold value.

9. The method according to claim 1, further comprising the step of generating a warning signal or changing the operation of the wind turbine (10) when it is determined that the reliability of the azimuth measurement system is reduced.

10. The step of changing the operation of the wind turbine (10) according to claim 9 includes one or more of reducing the output level of the wind turbine (10), stopping or changing one or more control algorithms depending on the measured values of the azimuth measurement system.

11. The method according to claim 1, further comprising the step of determining whether the angular phase of the in-plane moment having the rotor rotation speed frequency of the one or more blades deviates from the measured angular phase by more than a second threshold value greater than the first threshold value.

12. The method according to claim 11, further comprising the step of interrupting the operation of the wind turbine (10) when the selected in-plane moment of the blade deviates from the theoretical in-plane moment of the blade by more than the second threshold value.

13. A wind turbine (10) including a wind turbine rotor (18) having a plurality of blades (22), a plurality of load sensors for measuring the loads on said blades (22), an azimuth measurement system for determining the angular position of said wind turbine rotor (18) in the rotor plane, a control system and said control system receives signals (400) from said load sensors during operation, receives signals (420) from said azimuth measurement system, determines (410) the in-plane moment for one or more of said blades, selects the in-plane moment having the rotor rotational speed frequency for said blades, compares (430) the phase angle of said selected in-plane moment with the measured azimuth phase angle, and generates a warning signal when the phase angle of said selected in-plane moment deviates from said measured azimuth phase angle by more than a predetermined threshold value. A wind turbine system configured as such.

14. Each of said blades (22) comprises a strain gauge, and optionally, said strain gauge is attached to measure loads in the edge direction and the flap direction, and optionally, said sensor is attached at or near the root portion of said blade (22). The system according to claim 13.

15. The azimuth measurement system comprises a rotary encoder. The system according to claim 13.

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